In general, an optical fiber has a thin colored layer called an ink layer as the outermost layer for identifying an optical fiber consisting of a glass fiber and a coating resin layer with which the glass fiber is covered (see, for example, Patent Literature 1).
The coating resin layer needs to have sufficient curability for protecting the glass fiber and preventing transmission loss of the optical fiber. For example, reducing the content of tin included in the coating resin layer has been studied in Patent Literature 2, in order that both of microbend resistance and low-temperature properties are satisfied.